Can I implement a cooperative multi-tasking system in VxWorks?

Question

A legacy embedded system is implemented using a cooperative multi-tasking scheduler.

The system essentially works along the following lines:

• Task A does work
• When Task A is done, it yields the processor.
• Task B gets the processor and does work.
• Task B yields
  ...
• Task n yields
• Task A gets scheduled and does work

One big Circular Queue: A -> B -> C -> ... -> n -> A

We are porting the system to a new platform and want to minimize system redesign.

Is there a way to implement that type of cooperative multi-tasking in vxWorks?

Answer 1

While VxWorks is a priority based OS, it is possible to implement this type of cooperative multi-tasking.

Simply put all the tasks at the same priority.
In your code, where you do your yield, simply insert a 'taskDelay(0);'

Note that you have to make sure the kernel time slicing is disabled (kernelTimeSlice(0)).

All tasks at the same priority are in a Queue. When a task yields, it gets put at the end of the queue. This would implement the type of algorithm described.